Regulation of immune and inflammatory responses in animals is important in disease management. Immune responses can be regulated by modifying the activity of immunoregulatory molecules and immune cells. Such immunoregulatory molecules include, for example, cytokines, chemokines as well as soluble and membrane-bound immunoglobulin molecules.
One type of immunoregulatory molecule is immunoglobulin, a class of which is immunoglobulin G (IgG). The DNA and amino acid sequences of IgG molecules from several species have been reported. Peptides derived from known IgG sequences have been used to generate antibodies which alter IgG function. In humans and mice, IgGs have been fairly well characterized. In general, IgGs have been characterized by function and not DNA similarity since DNA similarity is not a reliable indicator of function.
Another type of immunoregulatory molecule is interleuken-13 (IL-13). Interleukin-13 is a cytokine produced by activated type 2 helper cells (Th2 cells). IL-13 promotes growth and differentiation of B cells, and IL-13 inhibits the production of inflammatory cytokines such as interleukin-1 alpha, interleukin-1 beta, interleukin-6, interleukin-8, interleukin-10 and interleukin-12 (designated as IL-1α, IL-1β, IL-6, IL-8, IL-10 and IL-12, respectively), among others.
A cDNA encoding IL-13 was first isolated from the mouse in 1989 and the human homologue was isolated in 1993. The human IL-13 gene is located on chromosome 5 q 31 which is 12 kilobases (kb) upstream of the interleukin-4 (IL-4) gene. Given the close proximity of the two genes, it is not surprising that IL-13 and IL-4 proteins share 25% sequence identity in humans and 30% sequence identity in mice. IL-13 and IL-4 are often simultaneously produced (with other cytokines) by Th2 cells. Both IL-13 and IL-4 share functional characteristics, such as inhibiting the production of inflammatory cytokines, and up-regulating the MHC class II and CD23 expression on monocytes and/or macrophages in B cells. Furthermore, IL-4 and IL-13 induce the IgE class switch in human cells in vitro and trigger IgG and IgM synthesis.
Both IL-13 and IL-4 have long played a role in allergy and inflammation, but until recently it has been difficult to separate the roles of these cytokines. Th2 cells are important participants in allergic conditions; as Th2 cells differentiate they produce cytokines directly or signal other allergic effector cells which induce and maintain allergic inflammatory responses. It is proposed that an allergen stimulates Th2 cells to produce IL-13 and/or IL-4, which in turn binds to IL-4R and/or IL-13R, signaling induction of IgE synthesis on B cells. Allergen-specific IgE then binds to IgE receptors on mast cells and basophils activating these cells and causing release of mediators of allergic inflammation. Induction of allergen specific Th2 differentiation represents a hallmark of allergic disease because cytokines produced by these cells induce and maintain allergic inflammatory processes. Th2 cells selectively develop and expand in the presence of IL-4. In humans, IL-13 fails to induce Th2-cell differentiation due to the lack of functional IL-13 receptors on T cells. IL-13 and IL-4 both induce IgE synthesis on B cells though IL-13 appears to be less potent in humans.
IL-4 and IL-13 receptors (referred to as IL-4R and IL-13R, respectively) share structural homology, in that both receptor complexes contain the IL-4 receptor alpha (IL-4Rα) chain which is required for signal transduction. Binding of IL-13 or IL-4 to IL-4R and IL-13R results in comparable signaling pathways. For example, if monoclonal antibodies are directed against the IL-4Rα chain (part of both the IL-4 and IL-13R complexes) IL-4 and IL-13 activity would be inhibited. Inhibition of biological activity of either of these cytokines would cause downstream regulation changes suggesting the importance of IL-4R□ for signal transduction. IL-13R can also function as a second receptor for IL-4 in cases where the IL-4R complex is compromised.
IL-13R is expressed on many cell types such as B cells, monocytes, macrophages, basophils, eosinophils, mast cells, endothelial cells, keratinocytes and some types of tumor cells, but active receptors have not been found on human T cells or murine B cells. Generally IL-13R is present in high numbers and thought to bind IL-13 with high affinity. The human IL-13 receptor complex consists of the 140-kilodalton (kD) IL-4Rα chain, which binds IL-4 but not IL-13, and an IL-13 binding protein. cDNAs encoding two different IL-13Rα (designated as IL-13Rα1 and IL-13Rα2) proteins have been isolated from humans and mice. Human IL-13Rα1 consists of 427 amino acids and binds IL-13 with low affinity (kD˜4 nanomoles/Liter) while human IL-13Rα2 is a 380 amino acid protein, which binds IL-13 with high affinity (kD˜50 picomoles/Liter).
Differences in IL-13 and IL-13R have been observed between species. Functional IL-13R is found on B cells in humans, while no functional IL-13R is found on B cells in mice. As such, no IgE response can be elicited from mouse B cells, so the role of IL-13 in stimulating IgE synthesis in mice remains unclear. However, it has recently been shown that IL-4 deficient mice are able to produce IgE, presumably through an IL-13 and IL-4 independent pathway. Given the differences in IL-13 activity between human and mouse, there would be no way to predict the IL-13 activity in other species, including dogs. As such there remains a need for compounds and methods to regulate an immune response in dogs through manipulation of IL-13 and IL-13R activities. The present invention satisfies this need and provides related advantages.